Two-stage carburetor



Oct. 9, 1955 M, sMlTLl-:Y ET AL 2,766,024

TWO-STAGE CARBURETOR 3 Sheets-Sheet l Filed Jan. 8, 1953 INVENTOR.

@fray/vir Oct# 9 1956 M. L. SMH-LEY ETAL 2,766,024

Two-STAGE CARBURETOR 5 sheets-sheet 2 Filed Jan. 8, 1953 C. 9, 1956 M L l 5M|TLEY ET AL 2,765,024

TWO-STAGE CARBURETOR Filed Jan. 8, 1953 5 Sheets-Sheet 3 INVENTOR.

at arent 2,766,024 Patented Oct. 9, 1956 2,7 66,024! TWO-STAGE CARBURETOR Marion L. Smitley, Huntington Woods, and Melvin F. Sterner, Royal Gak, Mich., assignors to Holley Carburetor Company, Detroit, Mich., a corporation of Michigan Application January 8, 19513, Serial No. 330,328 1 Claim. (Cl. 261-23) In the operation of large 200 horsepower Iautomotive engines, two carburetors in parallel are used and the primary carburetor is opened first by the first throttle and the secondary throttle of the secondary carburetor is opened later by the first throttle. With automatic transmission, a mechanical connection between first and second throttle has proven entirely satisfactory. With the ordinary synchromesh transmission, a mechanical linkfound to be unsatisfactory.

The object of this invention is to provide an automatic control of the secondary carburetor in a two-stage carburetor when used with an ordinary synchromesh transmission.

If the throttle of the secondary carburetor is mechanically opened, there is the possibility that with both throttles wide open at low engine speed, poor distribution will result when the ordinary synchromesh transmission is used.

To delay the opening at rst, and to later regulate the rate of opening by the road load, is the object of this invention. If manifold suction is applied to keep the throttle of the secondary carburetor closed, and if the suction just downstream of the lip of the first throttle (where suction is much greater than manifold suction) is applied to a diaphragm chamber to open the secondary throttle, then at low load`e. g. when accelerating on a level boulevard-the second throttle is all set to open long before the first throttle is wide open. As the iirst throttle is opened, the suction at a first restriction near the upstream lip of the first throttle remains relatively high and unregulated, and would open the second throttle much too soon. To regulate this suction below the lip of the first throttle as it opens, a

passage leading to a diaphragm chamber. This second hole bleeds air from the main air passage from a point (about 1/2" above the first hole) and thus, reduces the suction at the lip right after the initial throttle opening. Later on, as the throttle continues to open, the suction at the second opening increases and when half` open equals and exceeds the suction at the rst opening. Meanwhile, the manifold suction decreases so that the second throttle can follow and anticipate the motion of the first throttle and open after first throttle is half open. The second throttle is thus opened wide before the first throttle is wide open.

Figure l shows the preferred form of my invention.

Figure 2 shows an alternative construction.

Figure 3 shows the back view of Figure 2.

Figures 4, 5, 6 and 7 show alternative constructions.

In Figure l:

12 is the first throttle of the primary carburetor 14.

is the second throttle of the secondary carburetor 16.

Throttle 10 is unequally divided so that the suction in inlet manifold 18 holds throttle 10 shut when the engine is idling (both throttles shut).

20 is the diaphragm, the motion of which opens throttle 10 through linkage 11.

30 is the restricted orifice near the upstream lip of throttle 12.

32 is the second restricted orifice near 30. .n

22 is the spring which assists in keeping the throttle 10 closed.

24 is the casing which forms with the diaphragm 20 a vacuum chamber 26.

28 is the vacuum pipe leading from chamber 26 to th openings 30 and 32.

35 is the low speed tube of carburetor 14.

37 and 39 are the two low speed outlets from 35.

41 is the choke tube located in 34 which is the ait entrance 34 of carburetor 14.

Openings 32 and 30 are just upstream of the lip of the throttle 12 so that as the throttle 12 is opened, the suction in chamber 26 rises. 32 is in line with the throttle l2 when throttle 12 is half open.

The dimensions that have been found satisfactory for one installation (for 1/2 of a 200 horsepower engine):

Unbalance of throttle 10:0.055 in 1.3125 diameter Dimension of 30=0.046" Dimension of 32=0.05l"

Distance 30-32=1/.

Diameter of diaphragm 20:17/8 Y Leverage of spring 22:5/16 to 1/2 Minimum efiort of spring 22:12 ozs.

Maximum effort of spring 22:24 ozs.

In Figure 2:

An unrestricted opening 50 leading to the pipe 28 is located so that when the throttle of the primary carburetor has moved 50 from its idle position of 5 that is, when the throttle stands at 55 from the horizontal, the suction in 50 is at a maximum. The difficulty is that this location varies from 40 to 70 and a new location involves an expensive delay in changing the tool set up. With two restrictions, the diameters of these can be changed quickly and the equivalent of changing the location of opening 50 is cheaply made.

In Figure 3:

52 is the throttle lever for throttle 12 carrying 54 which is a bent link which engages a slot 56 in the throttle lever 58 for the throttle 10.

In Figure 4:

In this figure, the mechanical control shown in Figure 3 is omitted for the sake of clarity; and,

60 is the #l venturi of the primary carburetor.

62 is the #2 venturi of the secondary carburetor.

66 is a restriction in the walls of the throat of #2 venturi 62. i

68 is the pipe common to both restrictions 66 and 83.

83 is a restriction in the outlet from the primary carburetor located so as to become effective when #l throttle is opened to 55.

70 is a chamber with a diaphragm 72.

74 is a link leading to the #2 throttle 76 of the secondary carburetor 62 which throttle 76 is slightly olfset so as to be held closed by suction to keep the secondary carburetor out of action until actually needed.

78 is a tension spring which is connected to link 74 and assists the suction after #l throttle 80 In Figure 5: Here again, 60, 62, 76, 74, 78, 80, 70, 72, 68 have the same function as the corresponding parts in Fig. 4.

Here the #l throttle 80 has an important part to play.

transmitted through pipe 68 to act on diaphragm 72.

When this suction overcomes the spring 78 and the olfset of #2 throttle 76, then this #2 throttle 76 opens a third restriction 86 which is subjected to the suction downstream of the upstream lip of #2 throttle 76. This suction blends with suction generated by #l throttle yat restrictions 82 and 84. The cumulative effect through these three restrictions S2, 84 and 86 is such as to open the #2 throttle 76 at least as much as #l throttle 80 has been opened. The linkage shown in Fig. 3 limits this opening to an amount equal to the opening of #l throttle 80 so that the two throttles open in step with each other.

In Figure 6:

Here the parts 60, 62, 66, 68, 76, 78, 74, 70 and 80 have the same function as the corresponding parts shown and describedin Fig. 4 and restrictions 82 and 84 have the same functions as the parts so numbered in Fig. 5.

Figure 6 differs from Figure 4 in that restriction 83 of Figure 4 is replaced by two restrictions S2 and 84.

In Figure 7:

Here the parts 60, 62, 68, 70, 72, 74, 76, 78, S0, 82 and 84 have the same function as corresponding parts in Figures and 6. A restriction 69 in the walls of the throat 60 of the primary carburetor is connected into the pipe 68.

OPERATION Figure 1 The operation of the two carburetors 14 and 16 is similar except that primary carburetor 14 has a low speed tube 35 and choke 41 with the usual two speed fuel outlets 39 and 37. The choke valve 41 also acts as a nozzle, but this feature is no part of this invention which is restricted to the control of the second throttle by the first throttle.

Assume that the engine is running under closed throttle. The manifold suction holds throttle closed due to its offset. The l2 ounce pull of spring 22 at 5/16 radius holds throttle 10 shut. Then as the throttle 12 is opened, first the restriction 32, and later the restriction 30, cornes under the influence of the air flowing past the inclined butterfly throttle at the speed of sound around the tip of the upstream lip of throttle 12. This very high suction is great enough to overcome both the pull of spring 22 and the action of the lower manifold suction in 18 on the oifset throttle 10. Valve 10 is thus opened shortly after the throttle 12 has reached the position of approximately halfopen, provided that the road load permits the engine to accelerate normally. Any abnormal condition; e. ghead wind or steep grade-will permit throttle 12 to pass the half-way point and to permit the unbalanced throttle to remain closed (held by spring 22) so as to avoid wide open throttle low engine speed operation with both throttles wide open.

F gure 2 The operation of Figure 2 is the exact equivalent of the operation of Figure l except that the operation of determining the exact location of opening 50 is very diicult. in both cases, it should be noted that on the level road when the driver has opened the throttle from 5 idle position to 55 the second throttle is opened wide. Maximum speed is thus obtained. On approaching a hill, the car slows down and the driver opens the primary throttle 12 wide. The second throttle 10 remains closed and the hill is climbed on the primary carburetor functioning alone. On reaching level ground or descending a hill, the closing of the first throttle at firsts opens, and later causes the secondary throttle to close, as the lip of the throttle moves clock-wise and iirst raises, and then lowers, the suction at the two orices 30 and 32. The suction in pipe 28 is intermediate the two suctions in 32 and 30.

Figure 3 In Figure 3, when the throttle 12 is closed, link 54 engages the upper end of slot 56 and holds throttle 10 closed. When throttle 12. is wide open, throttle 10 may 4 still be closed; but, it could be wide open. When throttle 12 is half-open, throttle 10 may still be closed; but, it could be half-open.

Figure 4 Here the primary (#1) throttle 80 opens until at 55 (approximately) when the suction downstream of the up'- stream lip creates enough suction in chamber 70 to start #2 throttle 76 to move so as to open; and as 76 opens, suction in the secondary venturis 62 and restriction`66 also increases, so that throttle 76 continues to open as #l throttle 80 is opened provided the load is low enough to permit this operation.

Figure 5 After the throttle 80 brings the inuence of the throttle, brought under the thereupon begins the irst restriction 84 under then the restriction 82 is inuence of throttle 80. Throttle 76 to open when restriction 86 is subjected to suction downstream of upstream lip of throttle 76. #2 throttle 76 is then opened wide at light loads and high engine speeds.

Figure 6 Here again the operation is assisted, as in Figure 4, by the suction in the #2 venturi 62 which increases as #2 throttle 76 continues to open so that when #l throttle is wide open, #2 throttle 76 is also wide open due to the influence of venturi suction in the #2 carburetor 62 acting in conjunction with the restriction 66 leading to the chamber 70.

Figure 7 Here the suction created in the primary carburetor (transmitted through the primary venturi 60 at restriction 69) assists the suction on downstream side of #l throttle 80 acting through restrictions 82 and 84 to keep the #2 throttle 76 open so as to keep in step with the opening of the #l throttle 80 which is usually operated by hand.

What we claim is:

In `a two-stage carburetor for an internal combustion engine having a manually operated primary carburetor in parallel with a secondary carburetor which is opened automatically, both carburetors having an air entrance, a mixture outlet and a butterfly throttle in each outlet, a restricted opening in the wall of the mixture outlet of the primary carburetor located so as to be transferred from the atmospheric side to the engine suction side of the said butterfly throttle in said primary carburetor the moment it moves away from its idle position in the wall of the first mixture outlet and a second restriction adjacent the first restriction and located so as to be subjected to the engine suction when the first throttle is approximately one-half open, a diaphragm, a chamber associated therewith, linkage connecting the diaphragm with said throttle of said secondary carburetor, yieldable means holding said second throttle closed, a passage from said two restrictions to said diaphragm chamber and whereby the resultant suctions from the said two restrictions opens the throttle of said secondary carburetor, the suction existing at each restriction modifying the suction existing at the other restriction and in which there is a venturi in the air entrance to the primary carburetor, a third restricted opening, said opening being located in the wall of the throat thereof, a connection between said opening and said passage connecting the other two restrictions, the butterfly throttle of said secondary carburetor being unbalanced so that the engine suction opposes the opening movement of said secondary throttle.

References Cited in the tile of this patent UNITED STATES PATENTS 

